In a radar sensor for motor vehicles which is used, for example, for position finding of preceding vehicles and for distance and speed measurement, for example a frequency-modulated continuous wave (FMCW) radar, each channel contains at least one mixer which mixes the high-frequency signal (RF signal) received by the radar antenna with a signal of a local oscillator which is supplied via the oscillator port in order to generate an intermediate frequency signal as an output signal, whose frequency corresponds to the difference between the frequency of the transmitted oscillator signal and the frequency of the received RF signal. In newer radar sensors these mixers are formed by integrated components based on silicon-germanium, using so-called microwave monolithic integrated circuits (MMICs), for example.
A distinction is generally made between I/Q mixers, in which the real part of the down-mixed signal may be tapped at an I output and an imaginary part of this signal (quadrature) may be tapped at a Q output, and so-called in-phase mixers, in which only the real part may be tapped. Heretofore, primarily in-phase mixers have been used in radar sensors for motor vehicles.
Although I-Q mixers have the advantage of having a higher signal quality, and for certain applications they allow a reduction in the necessary computing power in the downstream evaluation path, on the other hand they have the disadvantage of requiring a doubling of the evaluation chain, resulting in increased costs for additional contact pads on the chip, bond transitions, preamplifiers, A/D converters, and the like.